(Newser)
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Florida officials say a mineral overdose is the probable cause of death for 21 Venezuelan-owned polo horses that fell ill as they prepared for a championship match earlier this month. The Florida Department of Agriculture and Consumer Services said today the animals likely overdosed on selenium, a common mineral that can be toxic in high doses.

The horses from the Lechuza Caracas team began collapsing as they were unloaded from trailers at the International Polo Club Palm Beach in Wellington. Some died at the scene and others hours later. All 21 horses were dead by the next day. The toxicology results say the animals had "significantly increased selenium levels." Necropsies previously revealed bleeding in the horses' lungs.